Context:
In this chapter, yet more core CSS knowledge has been thrown at you, much of which forms the bulk of all the CSS development you’ll do from now on. Grasping this basic knowledge of layout approaches will stand you in good stead for what is to follow. If you are not sure you’ve understood everything in the first three chapters, fear not. So long as you don’t tear them out, they’ll remain in place as a dip-in guide should you need to refresh your memory.
What does that adjective mean as used in that paragraph?